In the production process for a liquid crystal display panel and the like, two substrates for sandwiching a liquid crystal layer are produced separately, and then bonded with each other. Usually, an alignment mark is formed on each of the substrates, and the alignment mark is used for alignment in the process of bonding the substrates.
Conventionally, the alignment mark is formed by providing an exclusive-use film (which is exclusively for forming the alignment film) provided on an entire surface of the substrate under an alignment film, and patterning the exclusive-use film. Thus, formation of the alignment mark increases processing steps.
In order to form the alignment mark without increasing the processing steps, resist for forming a wiring pattern is used as the alignment mark in Japanese Publication for Unexamined Patent Application, Tokukaihei 1-92721 (publication date: Apr. 12, 1989).
According to a liquid crystal display unit in Japanese Publication for Unexamined Patent Application, Tokukaihei 1-92721 (publication date: Apr. 12, 1989), a mask part and an alignment mark part (a part to be used as the alignment mark) are formed simultaneously by using a resist layer (which functions as a mask in patterning an ITO (Indium Tin Oxide) film (wire) by development). After the wiring pattern is formed by development, only the mask part of the resist layer is removed, and the alignment mark is left. The alignment mark is used later for alignment.
Meanwhile, in a 2D/3D switching type liquid crystal display panel proposed recently (see, for example, U.S. Pat. No. 6,046,849 (Date of patent: Apr. 4, 2000)), a patterning phase difference plate is used as a parallax barrier. The phase difference plate includes an alignment film and a liquid crystal layer (which are provided on a substrate), and has different optical characteristics from region to region.
In producing the 2D/3D switching type liquid crystal display panel, it is necessary to align the patterning phase difference plate with a liquid crystal panel for generating a display image, and to bond the patterning phase difference plate and the liquid crystal panel. Therefore, there is a need for a method that does not increase the processing steps even if the alignment mark of the patterning phase difference plate is formed.
However, according to the arrangement of Japanese Publication for Unexamined Patent Application, Tokukaihei 1-92721 (publication date: Apr. 12, 1989), the resist layer, which is used for forming the wiring pattern, is also used for forming the alignment mark. Therefore, if the alignment mark is formed in a region where the liquid crystal layer is to be formed, the alignment mark remains as an inner surface of a cell (into which liquid crystal is to be injected) even after the substrates are bonded. As a result, the alignment mark directly contacts liquid crystal injected into the cell.
By nature, the resist used as the alignment mark is not highly resistant to solvent medium. Therefore, if the alignment mark is formed in such a position that the alignment mark directly contacts the liquid crystal, the resist is deformed by dissolving into the liquid crystal solution. This causes a problem that alignment cannot be performed at high accuracy.
If the alignment mark formation method in Japanese Publication for Unexamined Patent Application, Tokukaihei 1-92721 (publication date: Apr. 12, 1989) is applied to a substrate for use in a liquid crystal panel, the foregoing problem can be solved by forming the alignment mark in a region other than the liquid crystal layer. However, the alignment mark formation method in Japanese Publication for Unexamined Patent Application, Tokukaihei 1-92721 (publication date: Apr. 12, 1989) cannot be applied to the patterning phase difference plate in U.S. Pat. No. 6,046,849 (Date of patent: Apr. 4, 2000), because the liquid crystal layer is formed on an entire surface of the substrate.
A person with an ordinary viewing field perceives images from two different points of view, because two eyes of the person are spatially separated from each other at the head. A human brain recognizes a 3D object from a parallax of the two images. By utilizing this mechanism, a liquid crystal display unit that performs 3D (three-dimensional) display has been developed. The 3D display is realized by causing a viewer to see an image from two different points of view (the right eye and the left eye) so as to generate a parallax.
In a liquid crystal display unit which performs 3D display, an image for the left eye and an image for the right eye to be displayed on a display screen are encoded according to e.g. color, polarization state, or display time, so as to supply images for different points of view to viewer's eyes. Then, the images are separated through an eye-glasses-type filtering system covering the viewer's eyes. In this way, the image for the left eye is supplied to the left eye only, and the image for the right eye is supplied to the right eye only.
In another liquid crystal display unit, a display panel 101 is combined with a parallax barrier 101 having a light-transmitting region and a light-shielding region arranged in a stripe shape. This allows a viewer to recognize a 3D image without using a visual assistance tool such as the filtering system (automatic 3D display). To an image for the right eye and an image for the left eye, which are generated by the display panel 101, the parallax barrier 102 gives certain angles (see FIG. 9(a)). From certain viewing regions in the space, the viewer can recognize a 3D image because the right eye can see only the image for the right eye, and the left eye can see only the image for the left eye (see FIG. 9(b)).
A liquid crystal display unit that performs automatic 3D display by thus using the parallax barrier is disclosed in U.S. Pat. No. 6,055,013 (Date of patent: Apr. 25, 2000), for example. In U.S. Pat. No. 6,055,013 (Date of patent: Apr. 25, 2000), a patterning phase difference plate is used as the parallax barrier.
A liquid crystal display unit disclosed in e.g. U.S. Pat. No. 6,046,849 (Date of patent: Apr. 4, 2000) includes the parallax barrier, and the liquid crystal display unit can electrically switch between 3D display and 2D display (two-dimensional display) because the liquid crystal display unit includes a switching liquid crystal layer or the like as a means of switching between a state where an effect of the parallax barrier is enabled and a state where the effect of the parallax barrier is disabled. That is, in accordance with ON/OFF of the switching liquid crystal layer, the unit of U.S. Pat. No. 6,046,849 (Date of patent: Apr. 4, 2000) performs 3D display when the effect of the parallax barrier is enabled, and performs 2D display when the effect of the parallax barrier is disabled.
However, this arrangement of the conventional 2D/3D switching type liquid crystal display unit has the following problem.
When the 2D/3D switching type liquid crystal display unit performs 3D display, light emitted from a light source passes through three active areas, i.e. the switching liquid crystal layer, the parallax barrier, and a display liquid crystal layer (a liquid crystal layer for generating a display screen). Therefore, the 2D/3D switching type liquid crystal display unit is realized by a transmissive liquid crystal display unit.
When the 2D/3D switching type liquid crystal display unit performs 2D display, it remains to be the case that the light emitted from the light source passes through the three active areas, i.e. the switching liquid crystal layer, the parallax barrier, and the display liquid crystal layer. The only difference is that the switching liquid crystal layer disables the parallax barrier.
Thus, in the 2D/3D switching type liquid crystal display unit, both in performing the 3D display and in performing the 2D display, the light emitted from the light source passes through the switching liquid crystal layer and the parallax barrier. Accordingly, light utilization efficiency is lowered. Therefore, power of a light source used in the 2D/3D switching type liquid crystal display unit needs to be higher than that of a light source used in a liquid crystal display unit which performs only 2D display or 3D display.
If a light source having higher power is used, it is particularly likely that the temperature of the liquid crystal layer (the display liquid crystal layer or the switching liquid crystal layer) provided closer to the light source increases, often to such an extent as to be equal to or higher than an ambient temperature. Therefore, there is a possibility that the liquid crystal layer provided closer to the light source does not function normally, thereby adversely affecting display operation, even at an ambient temperature which guarantees normal functions of the display liquid crystal layer and the switching liquid crystal layer.